In injection moulding processes, insert objects are frequently placed into the cavity in order to provide the injection-moulded product with a certain surface, for example, by means of an externally arranged foil. Examples of such products are yogurt cups or insulin syringes. The surfaces of such insert objects feature, for example, product-specific information, advertising, an expiration date and/or a barcode.
During the manufacture of an injection-moulded part, an error may occur and no insert object or more than one insert object is inadvertently placed into the cavity. A thusly manufactured injection-moulded part needs to be sorted out as a reject part after the manufacture.
A quality control is nowadays carried out after the manufacturing process in order to detect such errors, i.e., in order to determine the presence of an insert object or exactly one insert object. This is realized with the aid of cameras that create images of the finished injection-moulded products. Elaborate analyses of these images ultimately make it possible to determine whether the injection-moulded part features a desired insert object such that the injection-moulded part can be accordingly sorted as an acceptable part or a reject part.
U.S. Pat. No. 5,582,845 discloses a system that optically detects inserts by means of a camera before the injection moulding process is carried out. If the insert is missing, an alarm is activated and the system backs up and obtains an insert in order to correct the error. In DE 202008014027U1, JP 60219017, JP 60068918 and JP 63220967, an insert part likewise is respectively detected prior to the injection moulding process and the process is stopped if it is determined that such an insert part is missing. In this way, the manufacture of defective parts is prevented.
All these methods indeed successfully prevent the manufacture of defective parts without inserts. However, it was determined that the process needs to be started up anew after a machine stop such that other complications may arise, particularly due to varied temperatures of the molten masses, to cite just one example.
In addition, optical methods proved to be problematic because different gray scales need to be reliably evaluated and a complicated evaluation system is required for this purpose.